Project Summary The overall goal of this project is to advance our understanding of pneumococcal colonization. Pneumococcal diseases are major causes of morbidity and mortality in the United States and worldwide, and colonization of the nasopharynx is the first step for pneumococcal infections. While much is known about phenotypes and cellular processes associated with pneumococcal colonization, the molecules coordinating these processes are not well understood. Our preliminary work characterizing the Rgg144- Shp144 regulator-peptide signal transduction system has lead us to hypothesize that this system plays a pivotal role in orchestrating pneumococcal colonization. At a broad level, our work will provide insight into pneumococcal colonization and the Rgg family of signal transduction systems, widely distributed in streptococci and enterococci. At a specific level, we will determine which colonization-associated phenotypes are regulated by Rgg144 and establish whether Rgg144 mediates these phenotypes via regulation of the capsule (Aim 1). We will to identify specific residues associated with peptide-regulator interactions and with regulator-DNA interactions (Aim 2). We will reveal SHP144-derived peptides that act as agonists and antagonists in vitro and in vivo, for use in manipulating the system in basic functional studies as well as future drug development efforts (Aim 2 and 3). We will provide an in vivo characterization of Rgg144 expression and activity in multiple tissues over time using two different murine models of pneumococcal infection (Aim 3). Together, our findings will uncover the contribution of Rgg144 to transcriptional regulation of the capsule, advance our understanding of pneumococcal colonization, and shed light on the development of anti-pneumococcal therapies. The work is innovative in that it approaches the study of Rggs by generating a spatio-temporal map of Rgg144 expression and activity during infection.